This invention relates to new and useful improvements in bearing axial free play measurement and adjustment and is particularly suitable for spindle-mounted tapered roller wheel bearings.
Precision adjustment of wheel bearing free axial end play, particularly of truck, trailer and bus wheel hubs is very difficult and time consuming. So difficult that precise adjustment is seldom attained, because adjustment typically is attempted by feel or experienced guess.
It is generally recognized by those in the industry that adjustment of tapered roller wheel bearings, such as those used in wheel hubs on trucks, trailers, buses, etc., is a major consideration in preventing excessive wheel end component wear and early wheel end component failure, including catastrophic wheel loss. Wheel bearing axial end play setting effects bearing life and the usable service life of seals, brakes and tires.
It is generally acknowledged in heavy duty, over-the-road equipment that the ideal method of bearing adjustment is to utilize a dial indicator to determine the point of zero axial end play, and then to preload the bearing as much as 0.001 inch and no more, to obtain optimum bearing life. Prior art devices have rendered this a trial and error task, very time consuming, and often impossible outside the test laboratory. In practice, the time consuming trial and error method with a dial indicator is rarely used.
Excessive bearing preload rapidly destroys the bearings. Consequently, the industry has grown to accept 0.001 to 0.020 inch end play as tolerable, and 0.001 to 0.005 inch as preferred, providing it can be verified. In practice, verification using a dial indicator is rarely performed because of the difficulty and the incompatability of parts, tools and procedures. Because optimum bearing adjustment is so difficult and bearing failure is so costly, a portion of the transportation industry is experimenting with expensive, finely machined and pre-assembled hubs in the hope of reducing operational wheel end expenses.
The prior art in threaded wheel bearing retaining devices is separated into three types: double nut devices with either the inner or outer nut jammed against the other, which changes the adjustment; single nut devices; and single or double nuts highly torqued to retain a pre-assembled hub and bearing unit. These prior devices are secured from further rotation by bendable tabs, peening, set screws, threaded locking fluids, keyed circular clips, spring loaded locking mechanisms, or friction. The commonly practiced prior art methods of setting axial end play are torque, torque and back off or by feel. In each case the unsure mechanic, lacking a precision device and method, can only hope for success.
U.S. Pat. No. 4,812,094 is typical of prior art single nut devices. In this patent, the device requires fitting a socket tool over the nut, resulting in release of the locking tab so that the nut may be rotated freely while the tool is affixed. Accordingly, fine increments of rotation cannot be indexed. This procedure further inhibits the simultaneous use of a dial indicator, whereby determining the exact zero point of axial end play is very difficult, if not impossible. The device is capable only of very coarse, 150 adjustment increments, and the process of initially removing the nut socket incurs the risk of unintentional rotation of the unpinned nut.
Prior art methods are extremely friction sensitive. Thread tolerance, cut, irregularity, damage, contamination and many other variables affecting the friction in on-vehicle tapered roller wheel bearing adjustment, and each individual assembly is unique in its variation. Devices dependent upon torque averaging technique inherently set excessive axial end play on those assemblies having higher than the mean average friction. On a low friction assembly, using a torque technique excessively preloads and destroys the bearings. Prior methods are dependent on a severe surface lubricant to provide a broader, forgiving tolerance of the permissible mean adjustment range. This compromise in lack of precision, is costly.
The prior art provides no means to either monitor or readily measure wheel bearing axial clearance without partial disassembly. Improper adjustment of over-the-road equipment frequently leads to a bearing failure that may be detected audibly, by smoking brakes, by oil seal failure, by irregular tire wear, or by wheel end separation.